Distance measurement apparatus with detection timing correction

Abstract

An optical distance measurement apparatus that measures a distance using a round-trip time of light to an object includes an irradiator, a plurality of SPADs, a plurality of signal output units, a response number detector, a timing identifier, and a timing corrector. The response number detector detects a response number representing the number of responding one of the SPADs based on a pulse signal. The timing identifier identifies a temporary timing based on a state of variation in the response number along a time series and identifies a detection timing representing a timing when the optical distance measurement apparatus detects light in accordance with the temporary timing. The timing corrector acquires a correction time representing a time difference between the temporary timing and a true timing corresponding to a distance to an object and sets a timing corrected from the temporary timing by the correction time as the detection timing.

What is claimed is: 
     
       1. An optical distance measurement apparatus that measures a distance using a round-trip time of light to an object, the apparatus comprising:
 an irradiator configured to irradiate light waves to a region where the object is to be detected; 
 a plurality of SPADs each configured to respond to incidence of a photon including a reflected wave of the light waves; 
 a plurality of signal output units corresponding one-to-one to the plurality of SPADs, the plurality of signal output units being each configured to output a pulse signal every time when corresponding one of the SPADs responds; 
 a response number detector configured to detect a response number based on the pulse signal, the response number representing a number of the responding SPADs; 
 a timing identifier configured to identify, based on a state of variation in the response number along a time series, a temporary timing that satisfies conditions where the state of variation is set in advance and identify a detection timing in accordance with the temporary timing, the detection timing representing a timing when the optical distance measurement apparatus detects light; 
 a timing corrector configured to acquire a correction time representing a time difference between the temporary timing and a true timing corresponding to the distance to the object and set a timing corrected from the temporary timing by the correction time as the detection timing; 
 a correction calculator configured to calculate the correction time in accordance with a light-receiving environment for the optical distance measurement apparatus, wherein the correction calculator is configured to calculate the correction time by taking into account the response number at the temporary timing and a response duration representing a time period when the responding the SPADs continues to respond; and 
 a response measuring unit configured to monitor whether or not at least one of the SPADs responds to measure the response duration of the SPAD, wherein the correction calculator is configured to calculate the correction time by taking into account the response duration measured by the response measuring unit. 
 
     
     
       2. The optical distance measurement apparatus according to  claim 1 , wherein
 the timing identifier is configured to identify a timing when the response number reaches a maximum value as the temporary timing. 
 
     
     
       3. The optical distance measurement apparatus according to  claim 1 , wherein
 the correction calculator is configured to calculate the correction time in accordance with an intensity of light entering the optical distance measurement apparatus. 
 
     
     
       4. The optical distance measurement apparatus according to  claim 1 , wherein
 the correction calculator is configured to calculate the correction time by taking into account a response ratio relative to a total number of the SPADs. 
 
     
     
       5. The optical distance measurement apparatus according to  claim 1 , wherein
 the correction calculator is configured to calculate the correction time by taking into account an offset value representing the number of constantly responding SPADs. 
 
     
     
       6. The optical distance measurement apparatus according to  claim 1 , wherein
 the timing identifier is configured to identify the state of variation in the response number along the time series when the irradiator irradiates the light waves and identify the temporary timing based on an accumulated state of variation defined by accumulating the response number per unit of time from every irradiation of the light waves. 
 
     
     
       7. An optical distance measurement apparatus that measures a distance using a round-trip time of light to an object, the apparatus comprising:
 an irradiator configured to irradiate light waves to a region where the object is to be detected; 
 a plurality of SPADs each configured to respond to incidence of a photon including a reflected wave of the light waves; 
 a plurality of signal output units corresponding one-to-one to the plurality of SPADs, the plurality of signal output units being each configured to output a pulse signal every time when corresponding one of the SPADs responds; 
 a response number detector configured to detect a response number based on the pulse signal, the response number representing a number of the responding SPADs; 
 a timing identifier configured to identify, based on a state of variation in the response number along a time series, a temporary timing that satisfies conditions where the state of variation is set in advance and identify a detection timing in accordance with the temporary timing, the detection timing representing a timing when the optical distance measurement apparatus detects light; 
 a timing corrector configured to acquire a correction time representing a time difference between the temporary timing and a true timing corresponding to the distance to the object and set a timing corrected from the temporary timing by the correction time as the detection timing; and 
 a correction calculator configured to calculate the correction time in accordance with a light-receiving environment for the optical distance measurement apparatus, wherein the correction calculator is configured to calculate the correction time by taking into account the response number at the temporary timing and a response duration representing a time period when the responding the SPADs continues to respond; and 
 a temperature acquirer configured to acquire a temperature of at least one of the SPADs or an ambient temperature of the SPAD, wherein the correction calculator is configured to calculate the response duration in accordance with the temperature and calculate the correction time by taking the response duration into account. 
 
     
     
       8. The optical distance measurement apparatus according to  claim 7 , wherein
 the timing identifier is configured to identify a timing when the response number reaches a maximum value as the temporary timing. 
 
     
     
       9. The optical distance measurement apparatus according to  claim 7 , wherein
 the correction calculator is configured to calculate the correction time in accordance with an intensity of light entering the optical distance measurement apparatus. 
 
     
     
       10. The optical distance measurement apparatus according to  claim 7 , wherein
 the correction calculator is configured to calculate the correction time by taking into account a response ratio relative to a total number of the SPADs. 
 
     
     
       11. The optical distance measurement apparatus according to  claim 7 , wherein
 the correction calculator is configured to calculate the correction time by taking into account an offset value representing the number of constantly responding SPADs. 
 
     
     
       12. The optical distance measurement apparatus according to  claim 7 , wherein
 the timing identifier is configured to identify the state of variation in the response number along the time series when the irradiator irradiates the light waves and identify the temporary timing based on an accumulated state of variation defined by accumulating the response number per unit of time from every irradiation of the light waves.